Electric projection lamp having specially configurated envelope



June 13, 1967 E. H. WILEY 3,325,679

ELECTRIC PROJECTION LAMP HAVING SIECIALLY CONFIGURATED ENVELOPE, FiledFeb. 26, 1965 5 Sheets-Sheet 1 Figl.

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June 1967 E. H. WILEY 3,325,679

ELECTRIC PROJECTION LAMP HAVING SPECIALLY CONFIGURATED ENVELOPE FiledFeb. 26, 1965 5 Sheets-Sheet 2 H \iq His A td: FTWH lnven tov: Emme t lrl-LWiLe June 13, 1967 E. H. WILEY 3,325,679

ELECTRIC PROJECTION LAMP HAVING SPECIALLY CONFIGURATED ENVELOPE FiledFeb. 26, 1965 3 Sheets-Sheet 3 ITWVEBTTLOTI Emmett HWILe b9 Q27 [5 HisAfttO neg United States Patent M 3,325,679 ELECTRIC PROJECTION LAMPHAVING SPECIAL- LY CONFIGURATED ENVELOPE Emmett H. Wiley, Chesterland,Ohio, assignor to General Electric Company, a corporation of New YorkFiled Feb. 26, 1965, Ser. No. 435,589 6 Claims. (Cl. 315-71) Thisinvention relates generally to electric incandescent lamps comprising asealed glass bulb containing an incandescible filament, and moreparticularly to projection lamps of the type comprising an internalreflector.

In lamps designed for use in film projectors, such as movie projectionfor home use, restrictions on physical size are imposed by thecompactness of the housing in which the lamp is to be placed. In lampshaving an internal condenser reflector, this siZe limitation has adirect bearing on the performance of the condenser optics. To be fullyeffective as a condenser, a reflector must be as large in diameter asthe diameter of the cone generated by the limiting rays through the filmgate and lens aperture.

It is therefore an object of the present invention to provide a lamphaving a high degree of compactness and optical eflectiveness. It is afurther object to provide a novel bulb construction which permits movingthe reflector closer to the face of the bulb and therefore closer to theprojection aperture or film gate, whereby the same sized reflector willmore completely fill the lens aperture system and provide more light andbetter uniformity of illumination. It is a still further object toprovide this improved performance without changing the standard base andsocket location and preferably with no change in bulb dimension alongthe optical axis.

Briefly stated, and in accordance with one aspect of the invention, theabove objects are achieved by providing a bulb having a main tubularportion which is non-circular in cross-section and has a flattened frontface with the concave reflector facing said flattened face and havingits mouth in a plane adjacent to said face. In a preferred form, thecross-section of said main bulb portion may be described as being ofgenerally partial elliptical form with a rear face of partial circularform and sides flaring divergently toward the widened and flattenedfront face. In a further preferred form, the said main bulb portionterminates in a generally cylindrical neck portion having its axiscoincident with the axis of the circular rear face portion of the bulband sealed to a circular stem member which carries lead-in and supportwire members from which the reflector and filament are supported, withthe reflector offset from said axis toward the flattened front face ofthe bulb.

Further features and advantages of the invention will appear from thefollowing detailed description of species thereof and from the drawingswherein:

FIGS. 1 and 2 are fragmentary diagrammatic representations of opticalsystems of a movie projector;

FIG. 3 is a fragmentary diagrammatic representation of an optical systemincorporating a lamp in accordance with the invention;

FIGS. 4 and 5 are top and side elevation views of a lamp bulb prior toassembly with the rest of the lamp components and having a shape inaccordance with the invention;

FIGS. 6, 7 and 8 are a top view and two side views of another bulb shapein accordance with the invention;

FIGS. 9, 10 and 11 are respectively, side and front elevations and a topview of a completed lamp comprising the invention;

FIGS. 12 and 13 are rear and side elevations of a modified lamp having aballast filament behind the reflec- Patented June 13, 1967 tor inaccordance with a further feature of the invention; and

FIG. 14 is a section of the bulb of FIGS. 12 and 13 along the line 1414in FIG. 12.

In order to be fully effective as a condenser, a reflector (preferablyof ellipsoidal shape) must be as large in diameter as the diameter ofthe cone generated by the limiting rays through the film gate andprojection lens aperture. As illustrated in FIG. 1, for a distance Lbehind the film gate G, the reflector must be a minimum diameter D to befully effective. The greater the distance L from the film gate G, thelarger D must be.

In actual projection equipment there is usually some space requiredbehind the aperture or film gate for shutter mechanisms such that a lampbulb must be some minimum distance away from the aperture, usually onthe order of one-half to one and a half inches in an eight millimeterprojector. For the angle shown in FIG. 2 and the indicated allowance forshutter room S, a tubular cylindrical bulb would need to be of the sizeindicated as T20, 2 /2 inches in diameter, in order to enclose areflector large enough to fill the pick-up cone. Even this size bulbWould not allow the reflector clearance needed for normal manufacturingtolerances. Furthermore, this larger size and volume of merely largerbulbs are undesirable. For the smaller bulb sizes indicated in FIG. 2 bythe letter T (for tubular) followed by a numeral, the numeral designatesbulb diameter in eighths of an inch.

Referring to FIG. 3, in order to overcome these problems, thecross-sectional shape of the bulb B may be as represented n said FIG. 3.The bulb may be said to be bulged laterally to permit moving thereflector R close to the flattened front face f.

Referring to FIGS. 4 and 5, there is shown one form of bulb 1 prior toits assembly with the rest of the elements of the lamp, part of whichare indicated in broken lines in FIG. 5. As shown in FIG. 5, the bulb 1is of standard cylindrical (circular cross-section) form in the sealingarea indicated generally by the numeral 2 at the lower part of the bulbwhich has a longitudinal axis A. However, the main tubular or reflectorarea of the bulb indicated at 3' is bulged or expanded to allow adequateclearance for any reflector narrow enough to pass through thecylindrical portion 2. The main portion 3' of the bulb may be said to beof generally semi-elliptical shape in cross-section having a partialcircular rear face r (FIG. 4) joined by divergently flaring sides s tothe flattened front face at the opposite side of the axis A from therear face r.

Referring to FIGS. 9 to 11, the bulb 1 is joined to a so-called mountstructure comprising a glass stem 3 which may be of the flat disc-shapedor button stem type having lead-in and support conductors or pins 4, 5,6 and 7 (FIG. 5) sealed therethrough and which support the reflector 8and filament 9. The reflector 8 may be of a wellknown sheet metal typeor, as herein illustrated, of the glass base type such as shown inPatent 3,160,776 to Cardwell et al., and having on its inner concavesurface 10 (FIG. 10) a reflecting coating of metal such asvapordeposited aluminum or silver, or a multiple layer interference filmor dichroic coating which reflects light and transmits heat. Thereflector 8 is supported on laterally extending inner lead wire portions11 and 12 which also support the filament 9 in accurate predeterminedrelationship to the reflector 8. Each of the inner lead wires extendsthrough an opening in the reflector and is insulated therefrom in knownmanner by ceramic members 13 and 14 in said opening. The said lead wireportions 11 and 12 are, in turn, supported from and electricallyconnected to vertical inner lead wire portions 15 and 16 which may bewelded at respective ends to said lateral 6 and 7 by bowed or arcuatewire braces 17 and 18 which are welded at respective ends to therespective vertical lead wire portions 15 and 16 and to said pins 6 and7.

Each of said braces 17 and 18 is also preferably welded V to a wire stud19 (FIG. 9) having an end embedded in a boss 29 on the back surface ofthe glass base reflector 8. The stem 3 is also provided with a glassexhaust tube 21 (FIGS. and 9) for exhausting and gas filling the bulb 1.

In accordance with conventional practice, the mount assembly comprisingstem 3, reflector 8 and filament 9 and associated support structure, isfirst assembled with the filament 9 located in exact predeterminedrelationship to the reflector 8. It is then assembled in sealingrelation with the bulb 1 as indicated by the fragmentary showing of themount in FIG. 5, and the seal area 2 of the bulb is heated by gasburners to soften it and cause it to collapse down into a generallycylindrical neck portion 22 (FIG. 9) which has its axis coincident withthe bulb axis A and which is fusion sealed to the periphery of thecircular stem 3, the remainder of the bulb 1 below said stem 3 beingsevered by sharp gas flames. The bulb is then exhausted through the tube21 and filled with gas, such as nitrogen, after which the exhaust tubeis tipped off as shown in FIG. 9. A conventional base 23 may be securedby cement 24 to the bulb neck 22.

The reflector 8 has its sides cut away along parallel cords as bestshown at 25 in FIG. 10, in order to permit the use of a reflector of aslarge a diameter as possible to be passed through the cylindricalportion 2 of the bulb.

It will be noted from FIGS. 9 and 11 that the bulged bulb shape permitsmoving the reflector 8 closer to the face 1 of the bulb and thereforecloser to the aperture or film gate of the projection apparatus than inconventional cylindrical bulbs where the mouth of the reflector 8 issubstantially in a plane including the bulb axis A in order to permituse of a reflector of maximum size. For example, in a standard prior artlamp having a tubular bulb of about 1 /2 inches diameter, the face ofthe bulb is 1 inches from the aperture and the reflector of 1% inchesdiameter has its side cut away to leave a width of 1% inches. This widthleaves enough clearance in the bulb for manufacturing variabilitywithout the reflector touching the bulb if the reflector is placed nearthe center of the bulb. The reflector in this standard position does notcompletely fill the pick-up angle of an eight millimeter aperture and aone inch f/ 1.6 projection lens with which it is normally used.

on the other hand, in a lamp having a bulb shape as shown in FIGS. 4, 5and 9-11 and designated TB12, i.e., a tubular bulged shape with acylindrical portion 2 of about 1 /2 inch diameter, the width of thereflector '8 can be almost as large as the inside diameter of a T12 bulb(tubular, 1 /2 inch diameter) since the bulges allow generous clearanceonce the mount structure is in position in the bulb. The new bulb shapein this case permits locating the reflector about inch farther forwardso that the same sized reflector will more completely fill the lensaperture system and provide more light and better uniformity ofillumination.

, This improved performance is accomplished with no change from standardbase and socket location since the axes of the base 23 and bulb neck 22are coincident with permit larger reflectors to be used, the reflectorsize is still limited to that which will pass through the cylindrical 4portion 2 of the bulb. However, even larger reflectors may be used witha bulb 1a blown to the shape shown in FIGS. 6 to 8 wherein the entireeffective length (i.e, exclusive of the cullet 26) is of the same shapein crosssection as the bulb of FIGS. 4 and 5.

While the glass stem portion of the mount structure might be of a shapecorresponding to that of the crosssection of the bulb 1a, it ispreferable to use the same circular stem 3 of FIG. 9 so that thefinished lamp is the same as in FIGS. 9 to 11. For this purpose it ispreferable to form the bulb 1a with appropriate glass distribution orthickness which becomes uniform and round when driven down or contractedby the sealing fires to formthe neck portion 22 (FIG. 9). A glassdistribution in which the wall thickness is approximately inverselyproportional to its distance from the center line, or axis A, may beused.

More particularly, if the bulged or generally partial elliptical form isblown from a bulb of originally uniform circular cross-section tube, theglass walls in the bulged portions will be thinner than in the unbulgedrear face portion 1'. When the bulbs are placed on a sealing machine,with the mount structure 3, 8, 9, etc,, of FIGS. 9 to 11 located thereinas represented in FIG. 5, the bulged or expanded portions heat upfastest because they are thinner and shrink back in a manner thatreturns the glass to its original uniformity by the time it approachesthe button stem 3 (FIGS. 5 and 9) to which it is sealed. It will beunderstood that, in accordance with standard sealing practice, theassembly of bulb and mount. is rotated about its axis A relative to thesealing fires.

With bulbs of the shape shown in FIGS. 6 to 8, lamps have been made inwhich the reflector width is greater than the front to back (r to j)dimension of the bulb.

Lamps of the type shown in FIGS. 9 to 11, and employing a singlecoiled-coil filament in 150 watt rating, have satisfactory strength forprojection service in 21 volt designs; but not in volt designs. Foroperation directly from a 120 volt home current supply, the lamps areprovided with a ballast filament connected in series with the effectiveor main lighting filament. Such ballast filament has heretofore beenlocated at the front of the reflector in a vertical position below theeffective main filament.

In accordance with a further feature of the present invention, theballast filament of the high voltage type lamp is advantageously locatedbehind the reflector, this feature being made feasible because of thesubstantially greater space between the back of the reflector and therear face of the bulb in lamps made in accordance with the presentinvention.

Such a lamp is illustrated in FIGS. 12 and 13 wherein correspondingparts are designated by the same numerals as in FIGS. 9 to 11 with theaddition of the letter b. Thus, the bulb 1b is of a similar shape as thebulb 1 of FIGS. 9 to 11, but in this case it is of smaller sizedesignated TB12, i.e., a nominal diameter of 1 /2 inches, as compared toa TB14 or nominal diameter of 1% inches in FIGS. 9 to 11. In this case,the reflector 8b may be of the sheet metal type which may consist, for

example, of copper sheet which may be plated with nickel and then coatedwith vapor-deposited silver. The said reflector 8b may be supported fromthe inner ends of the front pins 6b and 7b (7b being behind 6b in FIG.13) through a curved brace wire 27 which is welded to said pins 6b and7b and is secured to tabs 28 on the reflector. Alternatively thereflector may be formed with tabs which are so spaced that they can welddirectly to front pins 6b and 7b. Of course, other variations arepossible. The inner lead wire portions 11b and12b are i in this caseshown by way of example as arranged one above the other, with thecoiled-coil filament 9b vertically disposed therebetween, and theyextend in known manner through openings in a ceramic insulator 13b in anopening at the apex of the reflector 8b. A rigid vertical lead wireportion 16b is welded to and between the inner end of the pin 5b and tothe end of the lead wire portion 11b at the rear of the insulator 13b.

In accordance with the invention, a ballast filament 29 of coiled-coiltungsten wire is located behind the reflector 8b and is electricallyconnected in series with the effective lighting filament 9b byconnection thereof between the lead wire 12b and the inner end of thepin 4b. A fuse wire 30 may also be interposed between one end of theballast filament 29 and the pin 4b and it may, if desired, be enclosedin an insulating tube 31 (FIG. 12) such as glass. In some cases, thefuse 30 may be omitted and the ballast filament 29 itself may functionso as to quench the arc formed upon burn-out of the filament 9b andthereby obviate the need for the fuse. In that case, the ballastfilament 29 may be connected directly between lead wire portion 12b andpin 4b.

The location of the ballast filament 29 behind the reflector 8b is madepracticable by virtue of the bulb shape and the location of thereflector in an offset position towards the front face fb, therebyleaving adequate room between the back of the reflector and the rearface rb for the filament and, if desired, a fuse.

The relocation of the ballast coil 29 to the rear of the reflectorprovides several advantages over the prior art structure wherein theballast filament extended vertically below the filament 9bfrom the leadwire 12b and was connected to a wire which extended laterally under thereflector 8b through a fuse wire section to the pin 4b. One advantage ofthe physical separation of the effective filament 9b and the ballastfilament 29 is that at burn-out of the filament 9b ions are formed whichstart an arc. With the prior art design, this arcing process continuedfrom the top of the main filament coil 9b down through the ballast coilto the fuse. This long sustained arc is detrimental and may generateexcessive heat and/or splatter metal on the relatively fragile bulb. Inthe present arrangement, as the main filament coil 9b fails andionization begins, the ballast coil 29' drops more voltage andsuppresses the arc in the main coil, assisting the fuse in stopping theare or, in some cases, eliminating the need for a fuse.

The location of the ballast coil 29 behind the reflector isolates itfrom the window area or front face fb of the bulb. This window areabecomes very hot and is susceptible to violent failure if contacted bymolten metal or arcs. With the present construction, any arcing may bequenched and fusing action may be confined behind the reflector awayfrom the critical front window area. It also avoids the reflectorforming unwanted images of the ballast filament which images can beannoying heat or light problems.

The new design also contains fewer parts and is more simple. The spacesinvolved are also much greater. Even in the absence of the fuse 30, ifthe ballast coil 29 arcs and burns out it will open into a gap manytimes longer than the prior art fuse. There is less loose metal atburnout. In the prior art design the sustained are converted both mainand ballast coils and the loose end of the fuse lead wire into hotprojectiles; this does not occur in the construction disclosed herein.

It will be understood by those skilled in the art that while structuraldetails of presently preferred species have been shown and describedherein, they may be widely modified within the true spirit and scope ofthe invention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric projection lamp comprising a glass bulb having a maintubular portion having a flattened front face portion and closed by aglass stem member sealed to the end thereof, a separate concavereflector within the main portion of said bulb and facing said flattenedfront face portion with its mouth adjacent to said face portion, afilament in predetermined relation to said reflector and between saidreflector and said flattened face portion of the bulb, current supplyand support members supporting said reflector and said filament andhaving portions thereof sealed in and supported from said stern member.

2. An electric projection lamp comprising a glass bulb having a maintubular portion terminating in a cylindrical neck portion closed by andsealed at its end to a circular stem member, said main tubular portionhaving a flattened front face portion, a separate concave reflectorwithin the main portion of said bulb and facing said flattened frontface portion with its mouth adjacent to said face portion, a filament inpredetermined relation to said reflector and between said reflector andsaid flattened face portion of the bulb, current supply and supportmembers supporting said reflector and said filament and having portionsthereof sealed in and supported from said stem member.

3. An electric projection lamp comprising a glass bulb having a maintubular portion of generally semi-elliptical cross-section with aflattened front face and terminating in a generally cylindrical neckportion, a circular glass stern member sealed to and closing said neckportion, a separate concave reflector within the main portion of saidbulb and facing said flattened front face with its mouth adjacentthereto and of a size closely approximating that of said front face, afilament in predetermined relation to said reflector and between saidreflector and said front face, and current supply and support memberssupporting said reflector and said filament and having portions sealedin and supported from said stem member.

4. An electric projection lamp comprising a glass bulb having a maintubular portion including a partial cylindrical rear face joined bydivergently flaring sides to a flattened front face, said front and rearfaces being at opposite sides of the longitudinal axis of saidcylindrical rear face, said main tubular portion terminating in areduced cylindrical neck portion having its axis coincident with saidlongitudinal axis, a circular glass stem member sealed to and closingsaid neck portion, a separate concave reflector within the main portionof said bulb and facing said flattened front face with its mouthadjacent thereto and offset substantially from said longitudinal axistoward said front face, a filament in predetermined relation to saidreflector and between said reflector and said front face, and currentsupply and support members supporting said reflector and said filamentand having portions thereof sealed in and supported from said sternmember.

5. An electric projection lamp comprising a glass bulb having a maintubular portion including a partial cylindrical rear face joined bydivergently flaring sides to a flattened front face, said front and rearfaces being at opposite sides of the longitudinal axis of saidcylindrical rear face, said main tubular portion terminating in areduced cylindrical neck portion having its axis coincident with saidlongitudinal axis, a circular glass stern member sealed to and closingsaid neck portion, a separate concave reflector within the main portionof said bulb and facing said flattened front face with its mouthadjacent thereto and offset substantially from said longitudinal axistoward said front face, a filament in predetermined relation to saidreflector and between said reflector and said front face, current supplyand support members supporting said reflector and said filament andhaving portions thereof sealed in and supported from said stem member,and a ballast filament located behind said reflector and electricallyconnected in series with the firstmentioned filament.

6. An electric projection lamp comprising a glass bulb having a maintubular portion of generally semi-elliptical cross-section with aflattened front face and terminating in a generally cylindrical neckportion, a circular glass stem member sealed to and closing said neckportion, a separate concave reflector within the main portion of 7' V 87 said bulb and offset toward and facing said flattened reflector andelectrically connected in series with the front face With its mouthadjacent thereto and of a size fil'st-melltloned filamentcloselyapproximating that of said front face, a filament NO mferences fled inpredetermined relation to said reflector and between said reflector andsaid front face, current supply and sup- JAMES w LAWRENCE, PrimaryExaminer port members supporting said reflector and said filament ARTHURGAUSS, Examiner.

and having portions sealed in and supported from said I stem member, anda ballast filament located behind said DEMEO! Amslam Exammer-

1. AN ELECTRIC PROJECTION LAMP COMPRISING A GLASS BULB HAVING A MAINTUBULAR PORTION HAVING A FLATTENED FRONT FACE PORTION AND CLOSED BY AGLASS STEM MEMBER SEALED TO THE END THEREOF, A SEPARATE CONCAVEREFLECTOR WITHIN THE MAIN PORTION OF SAID BULB AND FACING SAID FLATTENEDFRONT FACE PORTION WITH ITS MOUTH ADJACENT TO SAID FACE PORTION, AFILAMENT IN PREDETERMINED RELATION TO SAID REFLECTOR AND BETWEEN SAIDREFLECTOR AND SAID FLATTENED FACE PORTION OF THE BULB, CURRENT SUPPLYAND SUPPORT MEMBERS SUPPORTING SAID REFLECTOR AND SAID FILAMENT ANDHAVING PORTIONS THEREOF SEALED IN AND SUPPORTED FROM SAID STEM MEMBER.